A power-cable arrangement configured for carrying electric power generally comprises at least one protective envelope or casing. For example, it is possible for the energy conductors which originate at a generator to be provided individually with an insulating envelope and to be encased in a bundled state by a robust cable-protecting envelope made of HDPE (high-density polyethylene) or a similar plastic. A power-cable arrangement usually comprises a plurality of energy conductors, in particular made of copper, which are accommodated within the cable-protecting envelope and are embedded therein in a water-tight manner and such that they are protected against mechanical and chemical damage.
As far as a wind farm is concerned, a power-cable arrangement serves, for example, for transmitting power between wind turbines of the wind farm and/or between a wind turbine and an electric power transformer station. It is generally the case that the power cables leave the wind turbine in the lower region thereof, for example downstream of a switchgear unit arranged in the lower tower region or in the upper region of a load-bearing structure. This transition is usually referred to as “cable hangoff”. The load-bearing structure may be, for example, a tripod or pile foundation anchored in the sea bed. If the wind turbine is offshore, the power-cable arrangement is laid generally in the form of a submarine cable or offshore cable on or in the sea bed. In order to avoid the costs which would follow from the power-cable arrangement being damaged, said power-cable arrangement is generally also laid, in addition, in a further protective pipe.
The energy conductors of a power-cable arrangement are heated up in particular when they carry high-voltage current, and it is therefore usually desirable for the resulting heat to be dissipated. If a power-cable arrangement is laid in the form of a submarine cable, the portion which is laid under water is cooled relatively effectively. The power-cable arrangement of a wind turbine is usually laid such that the power-cable arrangement leaves the lower end of the tower and is routed into the sea. The tower is generally installed on a support—for example on a tripod and the lower end of the tower is therefore located some meters above the sea level. The tower, exposed to wave movement, is thus protected against impact. Accordingly, that portion of the power-cable arrangement which is exposed to the air is cooled only to an insufficient extent, in particular when the wind turbine is operating at full, or more or less full, power. As mentioned above, the temperature of a power cable rises under increased current load, and therefore the conductivity of the power cable decreases as the temperature rises. In order to be able to carry sufficient current even under high loading, it is therefore necessary for the diameter of the power cable to be appropriately large. Nevertheless, it is possible for disadvantageous “hot spots” to arise in the energy conductors, and the transmission of power is impaired. In order to avoid such “hot spots” in the power-cable arrangement of a wind turbine, it is necessary for the power of the latter to be restricted, and this, in turn, adversely affects the output of the wind farm. In order for it to be possible for action to be taken in good time, in the case of a known procedure, the cable temperatures are monitored using fiber-optic sensors. In particular in the case of a wind farm having a multiplicity of wind turbines, such temperature monitoring can be very complex and expensive.